Cameron Platt, admitted that her engagement to Lee Mitchell, 46 years older than her, “will come as a surprise to many”.
She made the announcement on Facebook with the pair having been secretly dating for six months.
Cameron posted a photo of the couple at a restaurant and another image of a diamond engagement ring.
She wrote that she met Prof Mitchell at top American university, Princeton, where he was head of English.
Cameron said: “I was taking his lecture course on Henry James and William Faulkner.
“Lee was little more than a stranger to me then but he captivated me with his brilliance, sensitivity and passion.
“His lectures changed forever the way that I think.”
She said that Prof Mitchell had become her “devoted mentor” by the time she graduated in English.
She went on to study a masters at Oxford where she realised her love for her the white-haired professor.
She continued: “I was surprised to find how much I still thought of Lee, and soon I understood that I felt something for him that I’d not fully acknowledged before.
“At the end of my two years in Oxford, after much reflection, and with encouragement from my wonderful friends, I resolved to shoot my shot.”
They had a date at New York’s Metropolitan Museum of Art where she wrote they were like “shy teens, eager but tentative”.
She went on: “Something then sprouted from a seed that neither of us had known that we’d planted and we realised that the force of feeling that we’d had for each other and called by other names (admiration, wonder, devotion, gratitude) held within it the hope and the potential for love.”
Cameron, originally from Santa Barbara, California, said that they were now ready to make their relationship public.
She added: “Eventually it became impossible to deny how fully we feel/meant for each other and neither of us has looked back since.”